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Ford plans an aggressive expansion into over 100 cities in the next 18 months, according to Sunny Madra, vice president of Ford X, its group that develops new mobility services. Ford sees scooters as an affordable, accessible way to move around cities without polluting, congesting traffic or struggling to park.

San Francisco-based Spin launched a dockless bikesharing service just over a year ago, and pivoted to a scooter sharing business, which proved more profitable. It now operates in 13 cities and college campuses, and launches in Detroit Thursday. But it hasn't kept pace with rivals Bird and Lime, which have rapidly expanded, raised hundreds of millions of dollars and sometimes rankled cities with aggressive tactics.

Spin CEO Derrick Ko said joining Ford will allow it to play the long game, rather than rushing to expand to secure another funding round.

For Ford, the acquisition may protect it from a wave of new mobility options that threaten its core business of cars and trucks. It's not the only automaker taking notice.

Earlier this week, GM said it will sell electric bikes next year. Daimler will launch a scooter-sharing pilot in a Southern European city this year, and expand into Germany next year, according to a spokesman. And last week Tesla CEO Elon Musk said his company might make an electric bike.

"Automakers are seeing that rideshare, bikeshare and scootershare are taking the short trips, from zero to five miles," Horace Dediu, a tech analyst who hosts a popular mobility conference, told CNN Business. "It's important for them to get ahead of this game."

Bird and Lime have said they've completed 10 million rides each in the first year of operation, growing far faster than Uber and Lyft did.

Now car companies, scooter startups and analysts are trying to figure out how big the market is for micromobilty, a catch-all term for lightweight, electric transportation options like bikes and scooters.

Nearly half of all vehicle trips in the United States are under three miles, according to the US government's National Household Travel survey. Short trips are ideal for micromobility, according to experts, whether it's an electric bike, scooter, or a new option that hasn't arrived yet.

Ninebot, which supplies the scooters for Spin, Bird and Lime, plans to unveil an electric moped and a tiny electric car next year, according to Ninebot CEO Gao Lufeng.

"Consumers are demanding more personalized options," Lufeng said through an interpreter. "There's a lot more room for imagination."